This invention relates to organic transistors and inverters.
Organic thin-film transistors (OTFTs) have several advantages over traditional transistors, including, for example, low cost, low processing temperature, mechanical flexibility, and large area coverage. Applications of OTFTs in consumer electronics and optoelectronics include flat-panel display drivers, radio-frequency identification (RFID) tags, smart cards, and sensors.
Conventional OTFTs are designed using the architecture of a typical inorganic metal-oxide-semiconductor field-effect transistor, in which a source terminal and a drain terminal are usually formed on the same plane above or below the transistor's semiconductor layer. The performance of conventional OTFTs is generally influenced by two design parameters: channel length (L) and field-effect mobility (μFE). One characterization of the performance is the source-drain response time tSD, which can be determined by the following equation: tSD=L2/(μFE×VDD), where VDD is the supply voltage.
With conventional OTFTs, it is difficult to reduce this source-drain response time tSD to achieve high operation frequency. One difficulty, for example, is the low field-effect mobility μFE of organic semiconductors used in OTFTs. Another difficulty relates to the channel length of the OTFT, which cannot be easily shortened using nano-lithographic techniques. In cases where the channel length of an OTFT can be reduced to the order of sub-micrometers, the contact resistance between its semiconductor layer and electrodes becomes another factor that can affect the performance of this organic device.